Abstract: A memory management arrangement facilitates interprocess data transfers by eliminating the need to construct temporary mapping tables when performing the data transfer operation. The arrangement includes the use of multiple and concurrent mapping tables in conjunction with the transmission of mapping table indentification bits with each data transfer operation.

Abstract: The present invention addresses a timing synchronization problem which arises in tandem modem operation when a single codec strobed by a common sample clock is used for A/D and D/A signal conversion in a modem. Tandem modem operation is defined as a system application when two modems have their RS-232 interfaces directly connected to one another. In accordance with the present invention, a digital interpolator connected to the A/D converter in the modem effectively alters the timing phase of the A/D converter in response to first and second control signals. The first control signal is generated in response to an externally supplied clock and an internal modem clock and is representative of any perturbations in the externally supplied clock with respect to the internal modem clock.

Abstract: A data communications system wherein a plurality of stations each transmits data messages through a time-shared channel. In one embodiment of the invention, each data message is transmitted in either one of two alternative modes. In the first mode, a station transmits a data message at any time while in the second mode each station is assigned different times to transmit their data messages and transmission by that station is inhibited at other times. The mode of transmission is determined by a number of events. One such event is when a data message is successfully transmitted by a station and within a predetermined time interval thereafter that station has another data message to transmit. In another embodiment of the invention, a station is operative in the above-described first or second modes. The operative mode is modified to maintain a waiting or idle period between two successively transmitted data messages when the first of these two data messages has been successfully transmitted.

Abstract: The present invention covers the notion of determining signal dispersion characteristics, such as amplitude, phase and delay, by transmitting a training sequence. This training sequence includes a plurality of predetermined symbols and has a time duration at least equal to the expected range of the signal dispersion delay characteristic. At a receiver, the received training sequence is processed using correlation and signal replication and the aforesaid signal dispersion characteristics are determined therefrom.

Abstract: The problem of noise enhancement is eliminated in communications systems by predistorting the amplitude of the transmitted information signal in a manner which compensates for the amplitude distortion introduced in a portion of the communications channel. In the disclosed embodiments, the communications system includes two signal transceivers which communicate with one another through a communications channel. The communications channel includes two-wire subscriber loops adjacent to each signal transceiver with a four-wire transmission path disposed between the subscriber loops. Each transceiver transmits an information signal which, depending on the system noise characteristics, is predistorted to compensate for all or a portion of the amplitude distortion introduced in a subscriber loop adjacent to that signal transceiver. The predistortion necessary to provide such compensation is determined at each transceiver in response to received signals at that transceiver.

Abstract: In a communications system having components which are interconnected via communications links, the system is provided with capability of responding to the application of a predetermined test signal to a link with information which identifies that link. Such information can take a variety of forms including the name of one or more persons assigned to use the link, and/or the telephone number or numbers associated with the link. This capability greatly reduces the time and expense associated with the maintenance and testing of a variety of communications systems, such as PBXs and central office switching machines.

Abstract: Frequency synthesis apparatus for providing a desired frequency which is greater than and a fractional multiple, N/M, of a reference signal frequency utilizes a fractional multiplier in the feedback path of a phase-locked loop. The fractional multiplier provides a multiplication of M/N on the feedback signal. Advantageously, this technique can be utilized in either analog or digitally-implemented phase-locked loops and can be coupled with the use of a fractional multiplier in the feedforward path of the digitally-implemented phase-locked loop to improve jitter performance.

Abstract: A structure for providing an N by N optical switch includes input and output structures disposed on either side of a planar electronic shutter array. Each of the input and output structures, which respectively provide optical signal splitting and combining, is realized by the stacking of N molded optical elements. Each element is formed of a plurality of molded materials with one providing an optical waveguide and the other providing a supporting structure for such waveguides. Advantageously, both the input and output structures utilize the same molded optical element and are fabricated in an identical manner. After such fabrication, the one structure to be designated as the output structure is rotated 90 degrees with respect to the input structure prior to abutment against the planar electronic shutter array.

Abstract: In an arrangement wherein an inquiry and a choice of respones thereto are displayed on a CRT screen, a selection is made by holding a touch-screen device against the area of the screen corresponding to the desired response. Such a touch-screen device is designed to have an inductive coil in its tip. When an electron beam which scans the CRT screen sweeps across the tip of the touch-screen device, an electrical signal is induced on the coil. The touch-position or the selection is determined based on a knowledge of the position of the electron beam on the screen at the time of the electrical signal induction.

Abstract: A multipurpose bus connects subsets of intercommunicating modular circuit packs in a complex electrical system. An individual one of the subsets may use the bus leads to transport signals differently from the other subsets. Each of the subsets of the circuit packs is selected to use the bus in particular time intervals. The subset, thus selected, uses the bus leads the way its own protocol governs during those particular time intervals and otherwise ignores the bus.

Abstract: In a telephone local loop transmission arrangement, data is communicated from the customer premises to the central office utilizing a multidimensional, passband signal illustratively at 480 kb/s. Specifically, the transmitted signal is encoded in a trellis code and precoded using a generalized partial response filter. The received signal is processed by a circuitry that implements a trellis decoding in combination with nonlinear filtering.

Abstract: In a dual-duplex system wherein the communications channels have associated propagation delays which are typically different from one another, equalizers are connected to operate upon the signal received from each channel. To synchronize the operation of these equalizers to each other, the coefficients of each equalizer are updated when the training sequence is received from at least one of the communications channels. The sequence of symbol values in the training sequence may either be known or unknown to the receiver prior to transmission. When this sequence is detected, the coefficient updating circuit for each equalizer operates in response to a common reference signal. This reference signal includes a plurality of symbols and the value of each symbol is supplied at the same time to each equalizer coefficient updating circuit.

Abstract: An echo canceller which incorporates an overlapping look-up-and-add structure is suitable for cancelling both the linear and nonlinear components of an echo. In the well-known overlapping look-up-and-add structure, the cancellation provided is the sum of a plurality of memory outputs wherein each memory is addressed by an associated transmitted symbol in a sequence of symbols along with one symbol immediately preceding and/or one symbol immediately succeeding each associated symbol. In accordance with the present invention, this structure is modified so that each memory is addressed by the plurality of bits representative of an associated symbol in the sequence of symbols along with less than all of the bits representative of one or more symbols adjacent to the associated symbol in the sequence.

Abstract: At least one pair of areas on a circuit pack or substrate is allocated for the placement of electromagnetic interference (EMI) absorbing material, e.g., split ferrite cores. All or a portion of the conductor paths for the circuit are routed between pairs of the allocated areas. After the circuit pack is developed and tested, if EMI suppression is required, the EMI-absorbing material extends around the conductors passing between the pairs of allocated areas using holes formed through the allocated pairs of areas. Such holes are formed prior to circuit assembly or, alternatively, are formed only as needed after circuit testing. A clip is used to secure the EMI-absorbing material to the circuit pack. Advantageously, the insertion and securement of the EMI-absorbing material does not require any soldering or special manufacturing tools or fixtures. Accordingly, it can be readily provided in any manufacturing process.

Abstract: A synchronization scheme for use in digital communications systems selectively replaces data-representative symbols that would ordinarily be transmitted through a plurality of communications channels with associated replacement symbols that represent the data and provide a synchronization mechanism. In the receiver, the replacement symbols are detected and control circuitry which determines the difference in propagation delay between communications channels. Advantageously, this scheme can provide a determination of the propagation delay difference between communications channels while such channels are being used to transmit customer data and does not alter the timing or format of such data.

Abstract: A technique for generating the tap-weight coefficients for a signal dispersion cancelling filter utilizes circuitry which is responsive to received signal samples and generates a time-ordered sequence of derived signal samples. The tap-weight coefficient circuitry includes filters which operate in response to this sequence. One such filter is responsive to the derived signal samples in a first portion of the sequence after the time-order of the derived signal samples therein is reversed and another filter is responsive to the derived signal samples in a second predetermined portion of the sequence. This technique is applicable to a variety of communications systems including television and is particularly suitable for integrated circuit implementation.

Abstract: In a system where a signal constellation is used for data communications, signal points in the signal constellation are selected to represent incoming data. The signal points, thus selected, are transmitted through a channel. The signal constellation is divided into a plurality of regions each including an equal number of signal points. A coding scheme is employed to ensure that signal points within any one region are selected equiprobably, and the probability of selecting any signal point in one region is different from that in another region.

Abstract: In a communications system, a transmitted signal is typically impaired by phase jitter attributed to power line harmonics and ringing voltages present in a communications channel. In order to properly recover the transmitted signal, the phase jitter in a received signal needs to be eliminated. To this end, an infinite-impulse-response (IIR) filter arrangement is employed in a receiver to estimate the phase jitter and is followed by a demodulator which substantially removes the jitter based on the estimate. The transfer function of this IIR filter arrangement is a function of the autocorrelation of a phase error, the latter being indicative of the difference between the phase jitter in the received signal and the jitter estimate.

Abstract: A computer including a keyboard portion and a display portion is interconnected in a manner which provides dual positions operational. In one position the keyboard portion may be horizontally positioned to facilitate the entry of data via the keyboard. In the other position, the display portion may be horizontally positioned to facilitate the entry of data or graphic designs via the interaction of a graphics pen over the display. Advantageously, the interconnection mechanism which provides the two positions maintains the readability of the display and the keyboard portions in either of the two positions.

Abstract: In a telephone local loop transmission arrangement, data is communicated from the customer premises to the central office utilizing a multi-dimensional, passband signal illustratively at 480 kb/s. Specifically, the transmitted signal is encoded in a trellis code and precoded using a generalized partial response filter. The received signal is processed by a circuitry that implements a trellis decoding in combination with nonlinear filtering.